Field of the Invention
The present invention relates to a seal structure using a metal gasket. The seal structure according to the present invention is used, for example, an automobile-related field, or is used in the other fields.
Description of the Conventional Art
For example, in the metal gasket for the automobile, in preparation for such a condition that the automobile travels in a seaside area, there is a case that a neutral salt spray test is executed as a spec evaluation item. In this case, in the case that a casing in the other end to which the metal gasket is installed is made of an aluminum material (including an aluminum alloy, same as above), salt water is piled up in (attached to) a gap between the metal gasket and the casing, and corrosion (gap corrosion) of the aluminum material due to the salt water (difference in an ion concentration) is generated by repeating a dry condition and a wet condition. The metal gasket achieves a seal function on the basis of a reaction of a portion coming into contact with the casing, however, the seal function is deteriorated in the case that the corrosion portion of the casing passes through a seal line.
The corrosion is generated even in the case that the casing is made of an iron-based material, however, since the aluminum (Al) has a greater ionization tendency than the iron-based material (Fe), the aluminum tends to be corroded.Al3++3H2O→Al(OH)3+3H+